Diesel fuel



Patented Nov. 9, 1943 DIESEL FUEL Wayne A. Proell, Chicago, 111., assignor to Standard Oil Company, Chicago, 111., a corporation of Indiana No Drawing.

Application September 80, 1941, Serial No. 412,997

Claims., (c1. 44457) The present invention relates to improved Diesel fuels and methods for obtaining same.

It is well known that fuel oils for use in Diesel engines having the proper physical characteristics as to pour point, cloud point, viscosity and volatility can beimproved by nitrating the same in order to increase the cetane number thereof. The nitration of such fuel oils, while improving the cetane number, tends to decrease the stability of the oils by formLng an insoluble sediment which produces a haze and eventually a deposit while the fuel oils are in storage. By means of the present invention this sediment is effectively and economically removed from the fuel oil whereby a greatly stabilized fuel oil is produced. An important feature of this phase of the present invention lies in the fact that the cetane number of the fuel oil is not adversely affected by the treatment for removing the haze and deposit. j

An object of the present invention is to produce Diesel fuel oils having improved ignition characteristics together with improved stability characteristics. A further object of the invention is to provide a process whereby the above-mentioned advantages can be effectively and economically obtained.

A-still further object is to provide stable fuel oils which have been nitrated.

Another object of the invention is to provide. blends of fuel oils which possess satisfactory crease the cetane number thereof consists in treating the fuel oil with nitrogen oxides such as nitric oxide, nitrogen dioxide or a mixture of these ases or with nitric acid. When the fuel oil is treated with nitrogen oxides the process can be carried out at room temperature or higher temperatures. In order to obtain a maximum increase in the cetane number of the fuel oil the latter should be treated with from 0.2% to 1% of nitrogen oxides based on the weight of the fuel oil and preferably with about 0.8% of the oxides. This reaction proceeds fairly rapidly and can be effectively carried out by mixing the oil with sodium nitrite and a. mineral acid, suchas H2804, whereby nitrogen oxides will be formed in the oil and react therewith. Obviously nitric oxide and/or nitrogen dioxide may be bubbled through the oil if this is more desirable. If it is desired to supply thenitrogen oxides to the untreated fuel rather than from' them in situ, this may be' accomplished economically by using the oxides produced by catalyticallyoxidizing ammonia or by other well known means. The increase in cetane number will vary from 4 to 14, depending upon the quantity of nitrogen oxides employed and the time of treatment. This method of nitrating fuel oils is more effective when the fuel oil is of virgin stock as compared with cracked stocks. Nitrated fuel oils of the above physical characteristics and high cetane numbers. I

Other and more detailed objects will appear as the description of the invention proceeds.

Generally, uncracked or virgin stocks such as straight rungas oil of relatively high paraflinicity are characterized by good compression ignition properties, i. e. a cetane number of 45 or higher,

but these stocks do not possess satisfactory propertles as to pour point, cloud point, viscosity and character become hazy and deposit a sediment after standing for a. period of about 24 hours or longer. Although this haze and deposit may be removed by filtration, a second haze and deposit forms again while the oil is in storage. It is sometimes desirable to treat the nitrated fuel oil a with a dilute alkali wash such as a sodium carbonate solution in order to remove excess nitrovolatility. On the other hand thermally or catalytlcally cracked stocks such as cyclic gas oils do not possess good ignition properties, that is, theyhave a cetane number below but these stocks are characterized by suitablefpour point, cloud point. viscosity and volatility properties. It is therefore desirable to treat cracked stocks to im-' prove their ignition properties so that they can be used as fuel oils for Diesel engines. Also the cetane-number of virgin'stoclss can be improved by nitration of the stocks and then, if desired, they can be blended with nitrated or unnitrated gen oxides and acids which may be present in the nitrated fuel.

While the above-described process is most effective when treating virgin stocks, it is sometimes desirable to nitrate a Diesel fuel composed of cracked stock. It has been found however, that such stocks can be nitrated more effectively by treating the same with nitric acid, preferably in the presence of glacial aceticl acid, than with nitrogen oxides. In this case from about 0.1% to about 2% by weight of concentrated nitric acid and from about 0.1% to about 2% of glacial cracked fuel oils to produce Diesel fuel oils which will meet a wide variety of specifications.

One method of nltrating fuel oils in order to inacetic acid is added to the oil. This mixture is agitated at intervals for a period of from about two hours to about a week. A treatment of about 2 hours will raise the cetane number about 10 or 12. By using much larger amounts of treatin a ent; that is, up to of the weightof the part by nitrating a oil, an increase of 30 to 40 cetane numbers will be obtained if the treatment is continued for about a week. The degree of cetane improvement is, of course, controlled not only by the time of nitration but also by the concentration of the nitration agent. Following the nitration step the fuel oil is washed with water and dilute alkali, and filtered. The pour point and viscosity characteristics of lightly nitrated fuel oils, which are entirely suitable, are substantially unchanged during the nitration step. The finished fuel therefore has suitable physical characteristics as well as a suitable cetane rating. The acetic acid is not only used as a diluent for the nitric acid but also as an inhibitor against sludge formation which often occurs during the nitration of fuel oils with nitric acid. It has been found advisable to use about 3 parts of acetic acid for'every part of nitric acid. In some of the known processes the fuel oil is treated with a mixture of nitric acid plus sulfuric acid which forms large amounts of sludge. The use of acetic acid in place of the sulfuric acid does not decrease the nitrating effect and practically eliminates the formation of sludge.

Whenever highly cracked or virgin fuel oils are nitrated by the process described above or by any of the known processes a haze and eventually a deposit or sediment occurs in the finished product during storage. These oil-insoluble impurities appear after a relatively short period of storage and later a deposit forms in the bottom of the storage container. In the past this haze and deposit has been eliminated by filtration after it has formed or merely by aging and permitting the sediment to settle out following by decan-' tation. The filtration process removes only the sediment and haze which has formed at the time of filtration but does not prevent a fresh haze and sediment from forming during further storage. Even though the nitrated fuel has' been filtered, or aged settled and decanted, several times the haze and sediment recur. It istherefore highly desirable to eliminate not only the hazeand sediment which has formed but also those constituents which will form sediment and haze at a later time, that is, latent haze and sediment, in order to obtain a highly stable nitrated Diesel fuel. The exact nature of the sediment or deposit is not known but it is believed that the deposit consists of various kinds of nitroresins which are developed during the nitration treatment.

According to the present invention an effective and economical method is provided for dehazing andfor eliminating the sediment in nitrated fuel oils which has formed during early storage and also for eliminating latent haze and sediment or those components which will form sediment after longer periods of storage. Accordingly I propose to take a fuel oil which has been nitrated by any one of the preceding methods and dilute the same with a diluent which is soluble in oil but which rendersthe haze and sediment less soluble therein, such as low molecular weight normally liquid or gaseous paramn hydrocarbons, more particularly ethane, propane, butane, pentane, hexane or the'like or a mixture thereof at substantially normal temperatures.

In addition to securing a stable Diesel fuel, it is highly desirable to obtain a fuel having a low pour point. While this aim may be achieved in low pour point (i. e. cracked) fuel, it can also be achieved to a much greater degree and more economically by a combination process, in which tha Diesel fuel is treated with a hydrocarbon such as' propane at low temperatures in the approximate range of 10- F. to 70 F. and. preferably about 40 F. Such a step simultaneously dewaxes the fuel and precipitates theunstable nitroresins from the oil, giving a low pour point, high octane number product. This combination process is especially adaptable to paraffinic stocks. In special. cases it may be desirable to first treat the nitrated stock with propane or ethane or mixtures thereof at an elevated temperature, say within the range of F. to F. to remove resins and nitrated resins, and then flash off propane to chill the oil to a temperature within the range of 10 F. and 70 F. to dewax the stock. As a normal step, however, simultaneous dewaxing-deresining treatment will give most rapid settling of wax.

The amount of hydrocarbon diluent varies from about 0.5 to 10 volumes, based on the amount of fuel oil being treated. The mixture of fuel oil and diluent is settled for about one-half hour to about 24 hours. The haze and. deposit or nitroresinsare less soluble in the diluted oil than in the undiluted fuel oil and hence settle out rapidly. The sediment forming components are either converted into an insoluble sediment and settle out with the nitroresins or are themselves less soluble in the diluent and settle out without conversion. The fuel oil is then filtered to remove the sediment and sediment-forming"components. The resulting diluted clear oil is then distilled in order to remove the diluent which can be used over again. This treatment does not effect the increased cetane number obtained by the nitration step and the stability of the treated nitrated fuel oil is far greater than was previously obtainable. As a specific example of the foregoing, a highly cracked fuel oil stack was nitrated with a mix- ,ture of nitric acid and acetic acid for one week. The product was washed to remove excess acid and was then diluted with one volume of hexane. This mixture was allowed to settle for one hour, after which time the mixture was filtered to remove the sediment which was a pale redresinous ever, the amount of haze and deposit after the two months storage periods was less than the nitrated oil without hexane treatment showed after one week of storage. By increasing the dilution of the fuel oil with hexane or other low molecular weight alkane and by permitting the diluted fuel oil to settle for a longer period, the stability of the oil would be.even further increased.

The above data clearly show that the treatment not only facilitates removal of oil-insoluble impurities which have already formed but also those 7 latent impurities which cannot beremoved by filtration. I

For economical reasons it is sometimes desirable to prepare a Diesel fuel oil by blending various stocks together. As stated above, certain stocks such as virgin stocks, have a good cetane rating and a cetane number of 45 or higher, a cyclic gas oil from a thermal or a catalytic cracking process possessing suitable physical characteristics but a low cetane number which has been nitrated in accordance with the above-described processes and subsequently dehazed may be blended therewith. Likewise, when conditions dictate, a cyclic gas oil from a thermal or catalytic process characterized by a low cetane number of 45 or less but possessing suitable physical characteristics as to pour point, cloud point, viscosity and volatility may be blended with a similar cracked gas oil which has been nitrated and dehazed in order to improve the cetane number thereof. The proportions of the components of the above-mentioned blends may be varied, depending upon the ex'act characteris 'tics desired in the finished fuel oil blend.'

It will be clear from the foregoing description that various modifications and variations of the processes may be carried out without departing,

from the spirit of the invention.

While specific examples of the process have been described above these are not to be construed as limitations of the invention which is to be limited solely by the scope of the appended claims.

I claim:

1. The process for removing existent and latent oil-insoluble impurities in nitrated fuel oils comprising adding a low molecular weight alkane to i the oil to render the existent impurities substantially entirely oil-insoluble and to develop the latent impurities, and removing said impurities from the oil.

2. The process for removing existent and latent oil-insoluble impurities in nitrated fuel oils comprising adding hexane to the oil to render the ex-' istent impurities substantially entirely oil-insoluble and to develop the latent impurities and removing said impurities from the oil.

3. A process for removing existent and latent oil-insoluble impurities in nitrated fuel oils comprising adding from 0.5.to about 10 volumes of ame of hexane, settling the mixture for about one hour, filtering the mixture to remove said impurities and finally distilling the oil to remove the hexane therefrom.

6. The process for improving nitrated wax-containing Diesel fuel oil comprising adding from about 0.5 to about 10 volumes of a low molecular weight alkane to the oil to precipitate both existent and latent oil insoluble impuritiescaused by the nitration of the fuel, and lowering the temperature of the mixture to a temperature in the approximate range of 10F. to -70 F. to efiect precipitation of wax-and wax-like impurities in the oil whereby the fuel oil is stabilized and the perature of the mixture is effected by flashing off at least a portion of the low .moleeular weight alkane.

8. A process for improving nitrated .wax-con- I taining Diesel fuel oil comprising adding from about 0.5 toabout 10 volumes of a low molecular weight alkane to the oil to precipitate both existent and latent oil insoluble impurities caused by the nitration of the fuel oil, removing the impurities from the oil, lowering the temperature of the mixture to a temperature in the approximate range of 10 F. and -70 F. to effect precipitation of wax and wax-like impurities in the oil, and removing the wax and wax-like impurities from the oil, whereby the fuel oil is stabilized and the pour point thereof is lowered.

9. The process for improving nitrated wax-containing Diesel fuel oil comprising adding from about 0.5 to about -10 volumes of a low molecular weight alkane to the oil to precipitate both existent and latent oil insoluble impurities caused by the nitration of the fuel, lowering the temperature of the mixture to a temperature in the approximate range of 10 F. to 70 F. to effect precipitation of wax and wax-like impurities in the oil, removing both the'oil insoluble impurities caused by the nitration and the wax and wax-like impurities from the oil, whereby the fuel oil is stabilized and the pour point thereof is lowered.

10. The process for improving nitrated waxcontaining Diesel fuel oil comprising adding from about 0.5 to about 10 volumes of low molecular wax-like impurities in the oil, removing both the oil insoluble impurities caused by the nitration and the wax and wax-like impurities from the weight alkane having a temperature in the approximate range of 10 F. to F; to the oil likewise previously chilled to a temperature within the approximate range of 10 F. to --70 F.

to simultaneously precipitate from the alkane-oil mixture both existent and latent oil insoluble impurities caused by the nitration of. the fuel and oil, whereby the fuel oil is stabilized and the P point thereof is lowered.

WAYNE A. PRoEnn- Y 

